An RBS may have two or more receiving antenna branches. These branches are normally balanced meaning that the energy coming from each individual antenna branch is approximately the same as the energy coming from the other antenna branches. This is valid for both the signal energy and the interference energy, thus the antenna branches of the RBS experience similar Signal to Interference and Noise Ratio, SINR.
It may happen that the antenna branches are not balanced, or are imbalanced, due to different feeder attenuation, dissimilar filters or unequal number of filters in the different antenna branches. Also a failure in an antenna branch or variations in the radio environment may cause the antenna branches to be imbalanced.
A change in balancing of the antenna branches may affect the ability of the RBS to receive uplink transmissions which may result in calls being dropped or inefficient use of uplink resources, deteriorated quality experienced by a user of a UE or mobile telephone.